Efficient highly connected deployment units

ABSTRACT

Efficient and highly-scalable network solutions are provided that each utilize deployment units based on Clos networks, but in an environment such as a data center of Internet Protocol-based network. Each of the deployment units can include multiple stages of devices, where connections between devices are only made between stages and the deployment units are highly connected. In some embodiments, the level of connectivity between two stages can be reduced, providing available connections to add edge switches and additional host connections while keeping the same number of between-tier connections. In some embodiments, where deployment units (or other network groups) can be used at different levels to connect other deployment units, the edges of the deployment units can be fused to reduce the number of devices per host connection.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/826,586, entitled “Efficient Highly Connected Data Centers,” filedJun. 29, 2010 (now U.S. Pat. No. 8,406,128), of which the fulldisclosure of these applications is incorporated herein by reference forall purposes.

BACKGROUND

As an increasing number of applications and services are being madeavailable over networks such as the Internet, and increasingly utilizingsources such as networked data centers, an increasing number of content,application, and/or service providers are turning to technologies suchas cloud computing and Web services. In such environments, the hardwareand/or software used to provide access to data and/or electronicresources typically needs to be scalable to meet the needs of varioususers at any given time. A user or customer typically will rent, lease,or otherwise pay for access to resources, and thus does not have topurchase and maintain the hardware and/or software to provide access tothese resources.

Various approaches exist that enable resources such as data centers andInternet-Protocol (IP)-based networks to scale as the needs of thevarious users and applications increase. In some cases, this requiresthe purchase of large, expensive hardware that typically provides morecapacity than is immediately necessary. In other cases, less expensivehardware devices can be used, but in order to handle conventionalrouting protocols the number of devices needed to scale can be quitelarge and complex to install. For a large number of resources to beprovided, this can provide a significant expenditure and overhead, whichcan be undesirable in many instances.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which:

FIG. 1 illustrates an environment in which various embodiments can beimplemented;

FIG. 2 illustrates an example of a highly connected network design thatcan be used in accordance with various embodiments;

FIGS. 3( a) and 3(b) illustrate views of a Clos network style deploymentunit that can be utilized in accordance with various embodiments;

FIGS. 4( a) and 4(b) illustrate Clos-based network groups with differentlevels of oversubscription that can be used in accordance with variousembodiments;

FIGS. 5( a) and 5(b) illustrates a traditional three-tier Clos networkand a network of Clos groups, respectively, that can be used inaccordance with various embodiments;

FIG. 6 illustrates an example process for implementing a network of Closgroups that can be used in accordance with various embodiments;

FIG. 7 illustrates an approach to connecting deployment units that canbe used in accordance with various embodiments;

FIG. 8 illustrates an approach to fusing adjacent fabrics that can beused in accordance with various embodiments;

FIGS. 9( a) and 9(b) illustrate approaches to connecting Clos networksthat can be used in accordance with various embodiments;

FIG. 10 illustrates an approach to fusing Clos groups that can be usedin accordance with various embodiments;

FIG. 11 illustrates an approach to fusing Clos groups that can be usedin accordance with various embodiments; and

FIG. 12 illustrates an example process for implementing a network ofClos groups that can be used in accordance with various embodiments.

DETAILED DESCRIPTION

Systems and methods in accordance with various embodiments of thepresent disclosure may overcome one or more of the aforementioned andother deficiencies experienced in conventional approaches to connectingresources in an environment such as a data center, compute cloud, orInternet Protocol (IP)-based network. In particular, various embodimentsutilize groups of network switches and/or other networking devices toprovide an efficient and highly scalable network solution. The networkcan include a plurality of deployment units (or areas or Clos groups asdiscussed herein). Each of the deployment units can include multipletiers of devices, where connections between devices are only madebetween tiers and the deployment units are highly connected. Thedeployment units can be based on Clos networks, wherein each deploymentunit is fully connected.

In some embodiments, the level of connectivity between two tiers can bereduced, such that the devices of one tier are connected to less thanall the devices of another tier. While this will result in groups thatare not necessarily proper Clos networks, as there can beoversubscription and less than full connectivity, the groups stillmaintain many of the important properties of a Clos network. In oneembodiment, this amounts to each spine switch only being connected toone egress switch. Since removing these connections will result in openports on the spine switches, additional connections can be made to allowfor the installation of additional edge switches in the deployment unit.As the edge switches typically connect to a number of host machines orother computing devices, this approach will increase the number of hostconnections that can be made by the deployment unit while not increasingthe number of between-tier connections that need to be made. Such anapproach can improve the efficiency of the network.

In other embodiments, where deployment units (or other network groups)can be used at different levels to connect other deployment units, theedges of the deployment units can be fused to reduce the number ofdevices and thus improve efficiency. In some embodiments, one or moreegress switches of a lower level deployment unit can be “fused” with oneor more edge switches of a higher level deployment unit, whereby asingle switch can take the place of two switches per conventionalnetwork group approaches. In some cases, the fusing of edges of thedeployment units can allow deployment units to be “stacked” likebuilding blocks, providing for ease of scalability. By fusing, however,each block can include one less stage than would be used forconventional approaches.

Various other advantages and implementations are possible as discussedand suggested below with respect to the various embodiments.

FIG. 1 illustrates an example of an environment 100 for implementingaspects in accordance with various embodiments. As will be appreciated,although a Web-based environment is used for purposes of explanation,different environments may be used, as appropriate, to implement variousembodiments. The environment 100 shown includes both a testing ordevelopment portion (or side) and a production portion. The productionportion includes an electronic client device 102, which can include anyappropriate device operable to send and receive requests, messages, orinformation over an appropriate network 104 and convey information backto a user of the device. Examples of such client devices includepersonal computers, cell phones, handheld messaging devices, laptopcomputers, set-top boxes, personal data assistants, electronic bookreaders, and the like. The network can include any appropriate network,including an intranet, the Internet, a cellular network, a local areanetwork, or any other such network or combination thereof. Componentsused for such a system can depend at least in part upon the type ofnetwork and/or environment selected. Protocols and components forcommunicating via such a network are well known and will not bediscussed herein in detail. Communication over the network can beenabled by wired or wireless connections, and combinations thereof. Inthis example, the network includes the Internet, as the environmentincludes a Web server 106 for receiving requests and serving content inresponse thereto, although for other networks an alternative deviceserving a similar purpose could be used as would be apparent to one ofordinary skill in the art.

The illustrative environment includes at least one application server108 and a data store 110. It should be understood that there can beseveral application servers, layers, or other elements, processes, orcomponents, which may be chained or otherwise configured, which caninteract to perform tasks such as obtaining data from an appropriatedata store. As used herein the term “data store” refers to any device orcombination of devices capable of storing, accessing, and retrievingdata, which may include any combination and number of data servers,databases, data storage devices, and data storage media, in anystandard, distributed, or clustered environment. The application servercan include any appropriate hardware and software for integrating withthe data store as needed to execute aspects of one or more applicationsfor the client device, handling a majority of the data access andbusiness logic for an application. The application server providesaccess control services in cooperation with the data store, and is ableto generate content such as text, graphics, audio, and/or video to betransferred to the user, which may be served to the user by the Webserver in the form of HTML, XML, or another appropriate structuredlanguage in this example. The handling of all requests and responses, aswell as the delivery of content between the client device 102 and theapplication server 108, can be handled by the Web server. It should beunderstood that the Web and application servers are not required and aremerely example components, as structured code discussed herein can beexecuted on any appropriate device or computing device as discussedelsewhere herein. Further, the environment can be architected in such away that a test automation framework can be provided as a service towhich a user or application can subscribe. A test automation frameworkcan be provided as an implementation of any of the various testingpatterns discussed herein, although various other implementations can beused as well, as discussed or suggested herein.

The environment also includes a development and/or testing side, whichincludes a user device 118 allowing a user such as a developer, dataadministrator, or tester to access the system. The user device 118 canbe any appropriate device or machine, such as is described above withrespect to the client device 102. The environment also includes adevelopment server 120, which functions similar to the applicationserver 108 but typically runs code during development and testing beforethe code is deployed and executed on the production side and isaccessible to outside users, for example. In some embodiments, anapplication server can function as a development server, and separateproduction and testing storage may not be used.

The data store 110 can include several separate data tables, databases,or other data storage mechanisms and media for storing data relating toa particular aspect. For example, the data store illustrated includesmechanisms for storing production data 112 and user information 116,which can be used to serve content for the production side. The datastore also is shown to include a mechanism for storing testing data 114,which can be used with the user information for the testing side. Itshould be understood that there can be many other aspects that may needto be stored in the data store, such as for page image information andaccess right information, which can be stored in any of the above listedmechanisms as appropriate or in additional mechanisms in the data store110. The data store 110 is operable, through logic associated therewith,to receive instructions from the application server 108 or developmentserver 120, and obtain, update, or otherwise process data in responsethereto. In one example, a user might submit a search request for acertain type of item. In this case, the data store might access the userinformation to verify the identity of the user, and can access thecatalog detail information to obtain information about items of thattype. The information then can be returned to the user, such as in aresults listing on a Web page that the user is able to view via abrowser on the user device 102. Information for a particular item ofinterest can be viewed in a dedicated page or window of the browser.

Each server typically will include an operating system that providesexecutable program instructions for the general administration andoperation of that server, and typically will include a computer-readablemedium storing instructions that, when executed by a processor of theserver, allow the server to perform its intended functions. Suitableimplementations for the operating system and general functionality ofthe servers are known or commercially available, and are readilyimplemented by persons having ordinary skill in the art, particularly inlight of the disclosure herein.

The environment in one embodiment is a distributed computing environmentutilizing several computer systems and components that areinterconnected via communication links, using one or more computernetworks or direct connections. However, it will be appreciated by thoseof ordinary skill in the art that such a system could operate equallywell in a system having fewer or a greater number of components than areillustrated in FIG. 1. Thus, the depiction of the system 100 in FIG. 1should be taken as being illustrative in nature, and not limiting to thescope of the disclosure.

An environment such as that illustrated in FIG. 1 can be useful for anelectronic marketplace or compute cloud, for example, wherein multiplehosts might be used to perform tasks such as serving content, executinglarge-scale computations, or performing any of a number of other suchtasks. Some of these hosts may be configured to offer the samefunctionality, while other servers might be configured to perform atleast some different functions. The hosts can be grouped together intoclusters or other functional groups for the performance of specifictasks, such as may be provided as part of a data center, cloud computingoffering, or processing service. The electronic environment in suchcases might include additional components and/or other arrangements,such as those illustrated in the configuration 200 of FIG. 2, discussedin detail below.

For example, FIG. 2 illustrates an example configuration 200 thatrepresents a traditional hierarchical network design that can be used toroute requests to specific host machines or other such devices, in orderto provide users or applications with access to a variety of distributedresources. This example shows a typical design that can be used for adata center, wherein a source such as an end user device 202 orapplication 204 is able to send requests across a network 206, such asthe Internet, to be received by one or more components of the datacenter. Properties of various components of the network, such asprovisioned instances, etc., can be managed using at least onemanagement system, component, or service 220. In this example, therequests are received over the network to one of a plurality of coreswitches 208, but it should be understood that there can be any of anumber of other components between the network and the core switches asknown in the art. As traditional differentiators have substantiallydisappeared, the terms “switch” and “router” can be usedinterchangeably. For purposes of clarity and explanation this documentstandardizes on the term “switch,” but it should be understood this termas used also encompasses routers and other devices or components usedfor such purposes. Further, the switches can include any appropriateswitch, such as a multilayer switch that operates at different levels inan OSI (Open System Interconnection) reference model.

As illustrated, each core switch 208 is able to communicate with each ofa plurality of aggregation switches 210, 212, which in at least someembodiments are utilized in pairs. Utilizing aggregation switches inpairs provides a redundant capability in case one or the switchesexperiences a failure or is otherwise unavailable, such that the otherdevice can route traffic for the connected devices. Each pair ofaggregation switches 210, 212 is linked to a plurality of physical racks214, each of which typically contains a top of rack (TOR) or “access”switch 216 and a plurality of physical host machines 218, such as dataservers and other processing devices. As shown, each aggregation switchcan be connected to a number of different racks, each with a number ofhost machines. The links between the layers can each comprise redundantlinks, or link pairs, with separate links for inbound and outboundtraffic. If the network utilizes redundant 1 Gigabit Ethernet (GbE)links, for example, the total bandwidth per redundant link is 2 GbE.

As an additional benefit, the use of aggregation switch pairs enablesthe capability of a link to be exceeded during peak periods, forexample, wherein both aggregation switches can concurrently handle androute traffic. Each pair of aggregation switches can service a dedicatednumber of racks, such as 120 racks, based on factors such as capacity,number of ports, etc. There can be any appropriate number of aggregationswitches in a data center, such as six aggregation pairs. The trafficfrom the aggregation pairs can be aggregated by the core switches, whichcan pass the traffic “up and out” of the data center, such as backacross the network 206. In some embodiments, the core switches areprovided in pairs as well, for purposes including redundancy.

In some embodiments, such as high radix interconnection networksutilized for high-performance computing (HPC) or other such purposes,each physical rack can contain multiple switches. Instead of a singlephysical TOR switch connecting thirty-six hosts in a physical rack, forexample, each of three switches in the rack can act as a local TORswitch for a “logical” rack (a sub-rack of a physical rack or logicalgrouping of devices (hosts and/or switches) from multiple racks), witheach local TOR switch connecting twelve of the host machines. Thelogical racks can be implemented using physical or wireless switches indifferent embodiments. In some embodiments each of these switches withina high performance computing rack manages up to twelve servers, but thenumber can vary depending on factors such as the number of ports on eachswitch. For example, if a switch contains twenty-four ports, half ofthose ports typically will be host-facing and the other half will facethe external network. A design in accordance with one embodiment couldutilize seven racks with three switches in each, with each local TORswitch communicating (redundantly) with twelve servers, which wouldgenerally be equivalent to twenty-one separate racks each with a singleTOR switch communicating with twelve servers, for example. In subsequentfigures and description, it should be understood that physical orlogical racks can be used within the scope of the various embodiments.

The connectivity approach used for such a network can vary betweenembodiments. For example, FIGS. 3( a) and 3(b) illustrate a design basedon a Clos network approach, wherein there are twenty-one racks each withat least one TOR switch (actual or local), and each of the TOR switchesis connected to an array of twelve spine switches, which typically willbe located in another physical rack. The array of spine switchescorresponds to a “center” stage in a traditional Clos network design.Since there are twelve hosts, there are twelve “up” connections andtwelve “down” connections to the spine switches. The design thusprovides a high radix network based on a re-arrangeably non-blockingClos network.

The design presented illustrates a two-tier folded Clos network. As seenin the configuration 300 of FIG. 3( a), there are effectively two layersof switches: a layer of spine switches and a layer of edge switches.Three of the edge switches, however, can be utilized as egress switcheswhich pass data on to the network. FIG. 3( b) thus illustrates a logicalarrangement 350 of the switches, herein referred to as a “deploymentunit,” showing the three edge switches as egress switches which sit atthe “top” of the group of switches and pass data “up and out” of thedeployment unit. Each of the twelve spine switches can be thought of ashaving a port out the logical “back” side to one of the three egressswitches, but the three switches are simply one of the twenty-four edgeservers illustrated in a folded representation. The egress switchessimply have the only connections out of the deployment unit, while theremaining edge switches have connections to underlying devices. Alltraffic into and out of the deployment unit thus is routed through oneof the three egress switches, although different numbers of switches canbe used in different embodiments.

Even though the network may appear similar to the traditional coreswitch-based design of FIG. 2, the spine switches in this designfunction as core switches, but do not have any outbound connectivity.The layers of the deployment unit have fully meshed connectivity,however, provided by the spine switches. The deployment unit without theegress switches would function as a standalone network without anyexternal connectivity. Thus, some of the edge switches can be utilizedas egress switches as illustrated. Otherwise, the fact that some of theedge switches are illustrated on the top layer and some on the bottomlayer is meaningless from a network connectivity perspective withrespect to the spine switches and the other edge switches, and there isvery symmetric behavior. The data within the deployment unit can bepushed through a number of equidistant, fault-tolerant paths, providingthe re-arrangably non-blocking behavior. With the paths being symmetricand equidistant, all the switches can follow the same routing protocoland spread the traffic evenly without a lot of overhead or additionallogic. Further, the deployment units can be replicated multiple timeswithin a data center, for example, wherein a Clos-style networkeffectively manages traffic across all of the deployment units in thedata center.

An advantage of a high radix network or similar fat tree design is thatthe network can easily be scaled by adding additional deployment units,each connected using an aggregation fabric such as is described withrespect to FIG. 2. A potential downside, however, is that the number ofdevices needed to scale the deployment units can increase very quickly,which can significantly increase the cost of the network. In an examplewhere large data switches in a network are replaced with a designutilizing commodity switches in a high radix or other suchimplementation, the number of devices increases from around fifteenswitches to on the order of seven hundred to eight hundred switches.Commodity switches as used herein generally refer not only tomass-produced, off-the-shelf switches, but also refer to switches builtby low cost Just-In-Time (JIT) or on-demand manufacturers, typicallyusing “merchant silicon” or other relatively low-cost materials.Commodity switches typically are relatively simple, although morecomplex proprietary switches can be included as well.

Replacing the large switches with a number of smaller commodity switchesin this example, however, increases the number of Layer 3 switches thatspeak the appropriate routing protocol on the order of about fifty timesin one embodiment. Further, each of the switches will have to obtaininformation about all the other switches in the data center, as well asinformation about all the host devices connected to those switches, suchthat the amount of information that each switch needs to obtain andprocess is much higher than in certain conventional designs. Thus, whilea high radix interconnection network provides advantages such as ease ofscalability and high bandwidth capability, as well as a chance forsignificant cost savings, the complexity of the routing protocol growson the order of n² for a two-tier Clos-based network design, and on theorder of n⁴ for a three-tier Clos-based network, where n is the numberof ports on the devices used in each tier. For a large number of hosts,this can provide a significant expenditure and overhead, which can beundesirable in many instances.

FIG. 4( a) illustrates a traditional three-stage, two-tier Clos networkconfiguration 400 in an “unfolded” view, similar to that shown in FIG.3( b), here based on six-port switches wherein there are half the numberof spine switches 402 as there are edge 404 or “lea” switches, andwherein half of the edge switches function as egress switches 406. TheClos network is highly connected, as each device in each tier isconnected to each device in an adjacent tier. The devices of both tiersthus are fully connected, with no intra-tier connections within a tier.If all the available ports on all the edge switches were used to makehost connections, there would be no connection out of the Clos network.Thus, as discussed previously, connections to an external network 408typically would be made using the available ports of the egress switches406. In some cases, at least some of the egress switches are used toconnect to devices that sit between the Clos network and the externalnetwork, such as a set of core switches and/or an aggregation fabric. Ascan be seen, however, the tier 2 devices (here spine switches) nevermake connections to anything but tier 1 devices (here edge or egressswitches). Thus, in order to route host traffic out to the externalnetwork, the host would communicate with an edge switch, which wouldcommunicate to a spine switch, which would communicate with an egressswitch, which would pass the communication to the external network. Thethree communications correspond to the three stages of the Clos network.As should be understood, there can be any appropriate number of tiers ina Clos network using any appropriate type of switches, such as twelve,twenty-four, or forty-eight port switches. The number of devices in eachtier can depend at least in part upon the number of ports, as atraditional Clos is fully connected and non-blocking, and does not haveoversubscription at any tier. While figures with limited numbers ofdevices are shown for purposes of simplicity and explanation, it shouldbe understood that the basic concepts apply and scale accordingly.

A potential downside to conventional Clos networks is that the networkscan be very expensive to scale due to factors such as full connectivityand 1:1 oversubscription. For devices with many ports, there will bemany more spine switches that must connect to each of the edge andegress devices. By not having any oversubscription at any level, theoverhead (e.g., based on the number of switches) per host device can beprohibitively large. The efficiency of a data center can be measured inone respect by comparing the number of available host connections to thenumber of devices used to provide the networking fabric. Anotherefficiency measurement looks at the network costs (e.g., based on thenumber of cables and switches) per number of host connections available.

An approach in accordance with various embodiments can improve theefficiency of Clos-based data centers, making the networks morerealistic in scale. The approach introduces oversubscription between thespine switches and the egress switches, such as is shown in theconfiguration 450 of FIG. 4( b). In this example, the number of “up”connections between the tier 2 spine switches 402 and the tier 1 egressswitches 406 is reduced, with each spine switch 402 only being connectedto one respective egress switch 406. In other embodiments, each spineswitch can be connected to less than the total number of egressswitches, etc. By reducing the number of connections up to the egressswitches, each spine switch will have one or more open ports (twoavailable ports in this example) that can be used to make “down”connections to additional tier 1 edge switches 404, each of which willhave additional host connections 452 available for connecting additionalhost machines or other such devices. By introducing 5:1 oversubscriptionin the example (with each spine switch having one connection to theegress switch stage and five connections to the edge switch stage) thenumber of host connections has increased on the order of 60% while onlyincreasing the cost of the network by about 10% due to the cost foradditional devices. The efficiency of the network thus has increasedaccordingly. Such a design also can be recursed to develop largernetworks, such as a four-tier network with the same or similar designprinciples.

In a conventional Clos network, such as the conventional three-tier Closnetwork illustrated in FIG. 5( a), there would only be three edgedevices in each deployment unit in the first tier. There are three “up”connections for each edge device as illustrated. It is possible,however, to accomplish connectivity using only a single up connectionfrom each spine switch. If a single up connection is used, the extraunused connections on the second tier devices can be used to enableadditional edge switches in the first tier. The total number ofbetween-tier connections would be the same, as each device would stillbe utilizing all ports (six in this example) for routing host traffic.The total number of devices has increased, as well as the availablenumber of host ports as a result of those additional edge devices. Thenecessary size of the overall deployment has been reduced, however, asan additional number ports can be provided using the same number ofswitches.

As seen in the configuration 500 of FIG. 5( b), wherein a networkincludes multiple deployment units, each deployment unit 502, 504 (or atleast a portion of the units) can have oversubscription introduced toenable the introduction of additional edge devices. As with aconventional three-tier Clos, multiple deployment units can beintroduced up to the number of connections that are available from thetier 3 devices 506. In this example there can be up to six connectionsfor each of the devices, such that the deployment unit can be replicatedup to six times. All connections are still made between tiers, with alldevices in tiers 1 and 2 being fully connected. The connections 510 tothe network are shown as broken lines in FIG. 5( b), as the links to therest of the network can include additional components between theswitches shown and the network, such as at least a layer of edgeswitches between the tier 3 switches and the network. In this example,the devices of tier 3 represent the cross-bar, or the point ofconnectivity between deployment units. In a conventional Clos networkthere would be several connections 508, such as triple-replicatedconnections, but in this configuration there is no such replication.There is only one connection from each tier 2 device in a deploymentunit to each tier 3 device in the crossbar 506. When the number of(redundant) connections up to tier 3 is reduced (the “removed”connections illustrated by dotted lines 508), additional devices (e.g.,devices 4 and 5 in each deployment unit) can be added to tier 1 in eachdeployment unit using the available ports/connections as a result ofremoving the connections between tiers 2 and 3. Reducing the number ofconnections up to the tier 3 switches also enables the addition of thesecond deployment unit and, as indicated, will permit the addition of asmany deployment units as there are ports (e.g., 6 or 6-n, where n is thenumber of connections made to the rest of the network). As should beapparent, the connections to tier 3 are all between-tier connections,but utilize a different connectivity solution than the fully connectedsolution used between tiers 1 and 2.

A potentially significant advantage of utilizing such design principlesis that the layout of a network (e.g., data center) can be determinedmathematically based on specific constraints, such as a desired numberof host connections and desired level of efficiency. The designprinciples utilized can include, for example, fully connecting tierswithin a deployment unit, only utilizing connections between tiers,selecting a connectivity solution for each crossbar, etc. The designalso can depend on other factors discussed elsewhere herein. Forexample, the number of switches in the top layer of the deployment unitcan be up to half the number of ports on each device, such that 24-portswitches there can be up to twelve devices in the top layer, and for6-port devices there can be up to three devices in the top layer. Andthere can be a very clear demarcation of tiers throughout the datacenter, where the tiers are regular and/or consistent between deploymentunits and wherein traffic always moves according to a regular approachwithin the data center, such as always going from tier to tier along apath with a similar number of connections. Such an approach has addedbenefits, as the data center can guarantee aspects such as the lack oflooping paths, consistent path lengths, etc.

A further advantage is that such a connectivity approach can retain manyof the benefits of a traditional Clos network, while reducing the needfor additional devices to scale. Such an approach also can prevent theproviding of multiple full bandwidth connections that might not actuallybe needed a majority of the time. Various levels of oversubscription canbe introduced while retaining many aspects of a Clos network. Further,in a data center or IP-based context, for example, traffic between hostsmight never leave a deployment unit, such that the tolerance foroversubscription can be greater than in environments such as a publicswitched telephone network (PSTN), where all traffic typically passesacross each tier in the network. In the case of coordinatedcalculations, for example, hosts can primarily communicate with eachother for a period of time such that much of the aggregation or corelayers will not receive much if any traffic from those hosts.Conventional Clos principles do not take into account aspects such asthe locality of traffic.

The approach discussed with respect to FIG. 5( b) thus can be thought ofas using a crossbar to link together a pair of two-tier Clos networks,using a specific connection scheme, or taking a very structuredthree-tier Clos network (or multi-tier) and adding oversubscription intothe layers of the network. In some embodiments, however, there can bedifferent levels of oversubscription at different points in the datacenter network. For example, different deployment units can havedifferent levels of oversubscription with respect to the crossbar, andthus can have different numbers of edge devices and host ports. In oneexample, a deployment unit could have redundant links for a customerpaying for higher bandwidth. Different levels of oversubscription alsocould be used for other reasons, such as to handle different types ofinstances provisioned in the deployment units. Further, certain switcheshave intrinsic oversubscription, such as 3:2 oversubscription forcertain 48 port switches, such that the choice of switch also candictate the design of the data center to some extent.

FIG. 6 illustrates an example process 600 for improving the efficiencyof a Clos-based data center that can be used in accordance with oneembodiment. In this example, a set of Clos-based deployment units (e.g.,six replicated units) is provided, each being highly connected such thatconnections are only made between tiers and each device in a tier iscapable of being connected to each device in an adjacent tier 602. Alevel of oversubscription at the spine switches of tier 2 of thedeployment units is determined 604. Based at least in part upon thedetermined level of oversubscription, the number of connections to bemade between the spine switches and the egress switches of eachdeployment unit can be reduced 606. Utilizing the open ports on thespine switches as a result of reducing the number of connections up tothe egress switches, additional edge devices can be added to thedeployment units that are capable of being fully connected to the spineswitches using the newly available ports 608. All between-tierconnections can be performed for each deployment unit, wherein each tier1 switch is fully connected to each tier 2 switch, and each tier 2switch is connected to at least one tier 1 egress switch 610. The egressswitches of the deployment units can be connected to an external networkusing a crossbar 612, aggregation fabric, or other appropriate networkor set of connection devices, which may also be Clos-based. It should beunderstood that for the various processes discussed herein, there can befewer, additional, or alternative steps performed in varying orders, orin parallel, within the scope of the various embodiments.

As was illustrated in FIG. 5( b), for example, core switches can beconnected to each of the tier 2 devices in each of the deployment units.In some embodiments, however, at least some of the core switches couldbe connected directly to the tier 1 (edge) switches, as illustrated inthe example configuration 700 of FIG. 7. The tier 2 (spine) switches insuch a configuration then can be reserved to handle only local trafficwithin each deployment unit. The ports on the edge switches in thisconfiguration thus are not fully populated with host devices, as inprevious examples, as some of the ports are instead used to connect tothe core switches (or aggregation fabric of other networking). The tier3 switches 702 can be connected directly to the tier 1 switches 704,bypassing the tier 2 switches 706 which in this case only route trafficback and forth between the tier 1 switches. The cabling can be a littlemore complex, such as where each tier 1 switch is a TOR switch in a rackof host devices. Any traffic that goes from one deployment unit to theother, however, now does not go through any of the tier 2 switches. Suchan approach does not take away any bandwidth away from the localtraffic, and if each of the edge switches is connected to the core, suchas by using a redundant link, then a significant number of extra buffersare added that can be used to prevent congestion events. In aconfiguration with 21 edge switches per deployment unit, the number ofavailable buffers can approximately double if bypassing the tier 2switches and instead connecting each edge switch. In a configurationwith six such deployment units, there would be over 100 buffersavailable, which can be efficient for various traffic patterns.

An advantage to an approach such as that described with respect to FIG.7 is that the tier 3 switches can be connected directly to the tier 1switches, which can be advantageous for certain types of traffic, suchas where that traffic is destined for the computing devices connected tothe tier 1 switches. In a conventional scenario, the traffic betweendeployment units passes through tiers 3 and 2 before arriving at tier 1,which ties up tier 2 with unnecessary traffic. Connecting the tier 3switches directly to the tier 2 switches prevents tying up the bandwidthof the tier 2 switches with the traffic between tiers 1 and 3. Further,bypassing the tier 2 switches with such traffic enables the tier 2bandwidth to be guaranteed for other traffic, particularly the trafficwithin the deployment unit. The guaranteed amount of tier 2 bandwidthalso allows the system to be more deterministic about the availablebandwidth for the tier 1 host traffic. Since traffic between deploymentunits does not go through tier 2, a customer can buy an entiredeployment unit of capacity, with the guarantee that the customer willhave the dedicated use of all interconnect within that deployment unit.

Another advantage of the approach described with respect to FIG. 7 isthat cheaper switches, or switches with smaller buffers, can be used tohandle bursts of traffic, which enables the bursts to be spread aroundto many more switches, as there typically will be many more tier 1switches than tier 2 switches. Generally, there will be about twice asmany tier 1 switches as tier 2 switches. Thus, if the spine and/orexternal links are divided over the tier 1 switches, the system canwithstand a greater frequency and/or amount of bursts.

An approach in accordance with other embodiments can instead dedicate aportion of the edge or leaf switches of each deployment unit forpurposes of connectivity between deployment units. As illustrated in theexample configuration 800 of FIG. 8, a specified set of leaf switches802 can be dedicated and utilized to fully connect to the core switches804 or other such tier 3 devices. There can be host machines on many ofthe leaf switches, but two or more of the leaf switches can connect upto tier 3 switches 804 in various embodiments. In this example thededicated switches 802 have no hosts attached, and are used purely forconnectivity. One advantage to such an approach is that all the buffersin those switches are dedicated to connectivity, which might beadvantageous for certain traffic patterns. Such an approach also helpswith scaling efficiency in addition to buffer efficiency.

As can be seen, the dedicated leaf switches 802 and the core switches804 essentially form a separate deployment unit, or a fully connectedtwo-stage network. The two units are essentially fused, however, as thededicated switches 802 are each shared between the fabrics of thedeployment unit and the connecting fabric.

Thus, instead of spreading the links across all the tier 1 switches asin FIG. 7, two or more of the tier 1 switches can be dedicated to handleall of the connectivity out of the deployment unit (e.g., up to the tier3 or spine switches). Such an approach may not provide the bufferingbenefits of FIG. 7, as the only buffers being used are the buffers onthe dedicated switches, but an advantage can be obtained in that therecan be dedicated bandwidth on those switches. There is no contention, asthe dedicated switches are meant for connection traffic and there is nohost traffic on those switches, since there are no directly-connectedhosts. The system thus can be very precise as to the amount of bandwidthto be provided. Further, the resources on tier 2 do not have to be tiedup for the traffic between deployment units. Thus, the system canguarantee the amount of connectivity within a deployment unit as well asbetween or otherwise outside the deployment units, and can guarantee theamount of exit bandwidth. A tradeoff between selecting the approaches ofFIGS. 7 and 8 thus can involve whether the customer or system wants tooptimize for buffering (to spread or localize the traffic) and whetherto provide guarantees for intra- and/or inter-deployment unit trafficand/or bandwidth.

The concept of sharing switches can be extended to the deployment of adata center or IP-based network. As discussed above, a data center canbe comprised of multiple deployment units or other such groupings, eachof which can be based on a Clos-type network. In some cases, thedeployment units can themselves be connected using one or more Closnetwork-type groupings, enabling the data center to be built using a setof similar network units. For example, FIG. 9( a) illustrates aconventional approach 900 wherein multiple Clos network groups 902, 904can be combined to provide network connectivity for a plurality ofhosts. In such networks, each Clos group can comprise an integratedcircuit or other fixed device. Thus, the level of oversubscription,number of devices, or other such aspects cannot be changed within agrouping. As can be seen, the Clos groups can be connected by connectingone or more egress switches 906 of lower level Clos groups 904 with oneor more edge switches 908 of an upper level Clos group 902, which mighthave egress switches connected to a higher level Clos group or externalnetwork, for example. Such an approach enables the data center to bebuilt and/or scaled by adding additional Clos groups and connecting themappropriately.

While such an approach can provide for ease of scaling, there is someinefficiency built into such an approach. For example, consider theegress switch 906 of one of the lower level Clos groups 904 that isconnected to the edge switch 908 of the higher level Clos group 902. Theprimary purpose of the connections between the devices is simply totransfer information from one leaf switch to another. This results in aredundancy for each connection, as a single switch could perform thefunctions performed by the separate switches in the separate Closgroups.

Systems and methods in accordance with various embodiments can eliminatethis redundancy by utilizing a single switch 910 to effectively replacea pair of switches (and associated cabling) of the conventionalapproach, as illustrated in the example configuration 950 of FIG. 9( b).As discussed, the network groups can be built using several separateinstances of commodity hardware that are then physically connected, suchthat computing devices can be added and removed as desired. One of thedevices can be removed for each combination of Clos groups 902, 904, anda single switch 910 can effectively function as a leaf device for eachpair of connected Clos groups 902, 904. These separate groups, orfabrics, are no longer “Clos” networks per se, but maintain many of theadvantages of Clos networks as discussed above. The fabrics thus becomefused together as the fabrics share at least one device, whereby theedges of the fabrics are fused and the fabrics are connected edge toedge. Each of the shared devices can actively participate in the twofused groups when the routing protocols are laid on top of the shareddevice. Such an approach enables the hierarchy of two-tier networkgroups to be scaled while optimizing on the number of necessaryswitches.

While the example shown has a limited number of switches for purposes ofsimplicity, it should be understood that the ability to fuse fabrics cansave a significant number of switches as opposed to using conventionalClos groupings. For example, two tier Clos network based on 24-portswitches will have 288 host ports. The design must typically be createdup front with these host ports in mind. If a customer wants to add moreports, such as an additional 12 ports to have a total of 300, theconventional approach would require moving to a three-tier, five-stageClos network. A three-tier network, however, will require 720 24-portswitches, and will handle 3,456 host connections. Thus, for twelveadditional switches the network must add infrastructure to handle 3,456connections.

Systems and methods in accordance with various embodiments instead canutilize multiple Clos-based network groups, but effectively “fuse” atleast some of those groups in order to reduce the necessary number ofdevices. Further, oversubscription can be introduced to these fusedClos-based groups to further reduce the necessary number of networkdevices per host connection.

The approach described with respect to FIG. 9( b) can be beneficial inmany situations, but can have some potential disadvantages. For example,in the design some switches will be part of two network groups at thesame time, which can potentially lead to confusion with respect to thecabling, replacement, and maintenance of the network. Further, in theconfiguration of FIG. 9( b) there are still two egress switches in eachof the lower Clos groups that are not fused with the upper group, suchthat these either need to be fused or connected to another group orfabric. In some cases these egress switches could instead be used asedge switches to provide host connections, but then each Clos group onlyhas one egress switch to enable traffic to leave the group, which canlead to problems with congestion events, etc., in some circumstances.

As discussed, one approach is to fuse each of the egress switches of alower Clos group with one of edge switches of an upper Clos group. Whendoing this, the lower Clos group would effectively have only two stagesthat only belong to that group: the edge switches and the spineswitches. The egress switches would effectively be part of the uppergroup as well. As illustrated in the example configuration 1000 of FIG.10, the grouping of the deployment units or “Clos groups” can then beadjusted such that there are a plurality of “network blocks” that eachinclude two stages of devices. As can be seen, since the egress switchesare shared with the edge switches of a block to be connected “above”each network block, the blocks can effectively be deployed with only twostages of devices. Thus, the number of devices needed for each hostconnection is reduced.

A further advantage, however, is that network blocks can be added asneeded to increase the number of host connections, but the blocks areeach smaller than conventional Clos networks. The smaller blocks alsocan provide added flexibility. For example, the configuration in FIG. 10allows for oversubscription. For six port switches as used in theexample, the three spine switches can each connect to one of theedge/egress switches in the upper block, while still being fullyconnected to four edge devices in the same network block. Thus, anetwork can be scaled using building blocks of two-tier network groups,with some of the tier 1 switches being removed to provide links andbandwidth to connect to other deployment units. And the connectivity tothe other deployment units can itself also be another two-tier Clos-typenetwork. The approach thus allows for an arbitrary nesting of two-tierClos-type network groups.

As illustrated in the example configuration 1100 of FIG. 11, the spineswitches can be fully connected to the edge switches in the upper block,and fully connected to the edge switches in the same block, toessentially form a fully connected Clos network but effectivelyeliminating a full stage of devices. The network is scaled by providinga nested hierarchy of two-stage Clos-type network groups.

Further, as shown in FIG. 11, the network blocks can be stacked asneeded to scale the network, without the need to provide a full Closdeployment. The level of oversubscription can be used to control thewidth of a high radix network or similar fat tree network at each level.All the network blocks or “containers” can be identical in variousembodiments, such that the addition of any number of blocks would bestraightforward and each could be connected using the same approach. Inother embodiments, however, there can be different type of blocks thatcan be connected, such that different levels of oversubscription,connectivity, and other such aspects can be provided as desired.

FIG. 12 illustrates an example process 1200 for improving the efficiencyof a Clos-based data center that can be used in accordance with oneembodiment. In this example, a set of Clos-based deployment units (e.g.,six replicated units) is provided, each being highly connected such thatconnections are only made between stages and each device in a stage iscapable of being connected to each device in an adjacent stage 1202. Theconnections between each deployment unit and a higher-level networkgroup are determined 1204. In some embodiments, this higher-levelnetwork group may also be a Clos-based deployment unit. Based at leastin part upon the functionality of the leaf switches in the deploymentunits and the higher-level network group, at least one of the egressswitches of each deployment can be removed and the functionalityreplaced by one of the edge switches of the higher-level network group1206. The functionality of each such edge switch can be adjusted suchthat the edge switch functions as both an edge switch in thehigher-level network group and an egress switch in the respectivedeployment unit 1208. All between stage connections are made for eachdeployment unit 1210, wherein each device is connected to a device in anadjacent tier using at least one connection. The egress switches (orother such devices) of the higher-level network group can be connectedto an external network using a crossbar, aggregation fabric, or otherappropriate network or set of connection devices, which may also beClos-based 1212. Various alternatives and variations exist within thescope of the various embodiments.

As discussed above, the various embodiments can be implemented in a widevariety of operating environments, which in some cases can include oneor more user computers, computing devices, or processing devices whichcan be used to operate any of a number of applications. User or clientdevices can include any of a number of general purpose personalcomputers, such as desktop or laptop computers running a standardoperating system, as well as cellular, wireless, and handheld devicesrunning mobile software and capable of supporting a number of networkingand messaging protocols. Such a system also can include a number ofworkstations running any of a variety of commercially-availableoperating systems and other known applications for purposes such asdevelopment and database management. These devices also can includeother electronic devices, such as dummy terminals, thin-clients, gamingsystems, and other devices capable of communicating via a network.

Various aspects also can be implemented as part of at least one serviceor Web service, such as may be part of a service-oriented architecture.Services such as Web services can communicate using any appropriate typeof messaging, such as by using messages in extensible markup language(XML) format and exchanged using an appropriate protocol such as SOAP(derived from the “Simple Object Access Protocol”). Processes providedor executed by such services can be written in any appropriate language,such as the Web Services Description Language (WSDL). Using a languagesuch as WSDL allows for functionality such as the automated generationof client-side code in various SOAP frameworks.

Most embodiments utilize at least one network that would be familiar tothose skilled in the art for supporting communications using any of avariety of commercially-available protocols, such as TCP/IP, OSI, FTP,UPnP, NFS, CIFS, and AppleTalk. The network can be, for example, a localarea network, a wide-area network, a virtual private network, theInternet, an intranet, an extranet, a public switched telephone network,an infrared network, a wireless network, and any combination thereof.

In embodiments utilizing a Web server, the Web server can run any of avariety of server or mid-tier applications, including HTTP servers, FTPservers, CGI servers, data servers, Java servers, and businessapplication servers. The server(s) also may be capable of executingprograms or scripts in response requests from user devices, such as byexecuting one or more Web applications that may be implemented as one ormore scripts or programs written in any programming language, such asJava®, C, C# or C++, or any scripting language, such as Perl, Python, orTCL, as well as combinations thereof. The server(s) may also includedatabase servers, including without limitation those commerciallyavailable from Oracle®, Microsoft®, Sybase®, and IBM®.

The environment can include a variety of data stores and other memoryand storage media as discussed above. These can reside in a variety oflocations, such as on a storage medium local to (and/or resident in) oneor more of the computers or remote from any or all of the computersacross the network. In a particular set of embodiments, the informationmay reside in a storage-area network (“SAN”) familiar to those skilledin the art. Similarly, any necessary files for performing the functionsattributed to the computers, servers, or other network devices may bestored locally and/or remotely, as appropriate. Where a system includescomputerized devices, each such device can include hardware elementsthat may be electrically coupled via a bus, the elements including, forexample, at least one central processing unit (CPU), at least one inputdevice (e.g., a mouse, keyboard, controller, touch screen, or keypad),and at least one output device (e.g., a display device, printer, orspeaker). Such a system may also include one or more storage devices,such as disk drives, optical storage devices, and solid-state storagedevices such as random access memory (“RAM”) or read-only memory(“ROM”), as well as removable media devices, memory cards, flash cards,etc.

Such devices also can include a computer-readable storage media reader,a communications device (e.g., a modem, a network card (wireless orwired), an infrared communication device, etc.), and working memory asdescribed above. The computer-readable storage media reader can beconnected with, or configured to receive, a computer-readable storagemedium, representing remote, local, fixed, and/or removable storagedevices as well as storage media for temporarily and/or more permanentlycontaining, storing, transmitting, and retrieving computer-readableinformation. The system and various devices also typically will includea number of software applications, modules, services, or other elementslocated within at least one working memory device, including anoperating system and application programs, such as a client applicationor Web browser. It should be appreciated that alternate embodiments mayhave numerous variations from that described above. For example,customized hardware might also be used and/or particular elements mightbe implemented in hardware, software (including portable software, suchas applets), or both. Further, connection to other computing devicessuch as network input/output devices may be employed.

Storage media and computer readable media for containing code, orportions of code, can include any appropriate media known or used in theart, including storage media and communication media, such as but notlimited to volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage and/or transmissionof information such as computer readable instructions, data structures,program modules, or other data, including RAM, ROM, EEPROM, flash memoryor other memory technology, CD-ROM, digital versatile disk (DVD) orother optical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed bythe a system device. Based on the disclosure and teachings providedherein, a person of ordinary skill in the art will appreciate other waysand/or methods to implement the various embodiments.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the claims.

What is claimed is:
 1. A highly connected network deployment unit,comprising: a plurality of computing devices each operable to receive arequest and perform a computing operation; a first tier of edge switchesand egress switches, the plurality of computing devices directlyconnected to at least a portion of the edge switches; and a second tierof spine switches, each of the edge switches directly connected to eachof the spine switches, each of the egress switches connected to at leastone of the spine switches, each of the edge switches and the egressswitches capable of being directly connected to each of the spineswitches, wherein a number of egress switches to which each spine switchis directly connected is based at least in part upon a determined levelof oversubscription, and wherein any available ports on each spineswitch are capable of being used to add additional edge switches to thenetwork deployment unit, the additional edge switches increasing a totalnumber of host connections capable of being made by the networkdeployment unit.
 2. The network deployment unit of claim 1, wherein eachof at least a portion of the edge switches or the additional edgeswitches comprise a top of rack (TOR) switch connected to a portion ofthe plurality of computing devices in a network rack.
 3. The networkdeployment of claim 1, wherein the network deployment unit is connectedto an external network using a high radix interconnection network.
 4. Adeployment unit, comprising: a first tier of switches; and a second tierof switches, each of the first tier of switches capable of beingdirectly connected to each of the second tier of switches, a firstportion of the first tier of switches directly connected to each of thesecond tier of switches, each of a second portion of the first tier ofswitches directly connected to at least one of the second tier ofswitches, wherein any available ports on each of the second tier ofswitches are capable of being directly connected to additional switches,the additional switches increasing a total number of host connectionscapable of being made by the deployment unit.
 5. The deployment unit ofclaim 4, wherein a number of the second portion of the first tier ofswitches directly connected to the second tier of switches is based atleast in part upon a determined level of oversubscription.
 6. Thedeployment unit of claim 4, wherein at least one of the second portionof the first tier of switches directly connects out of the deploymentunit.
 7. The deployment unit of claim 4, further comprising: a thirdtier of switches, each of the third tier of switches directly connectingout of the deployment unit, wherein at least one of the first portion ofthe first tier of switches directly connects to at least one of thethird tier of switches, and wherein network traffic between deploymentunits bypasses the second tier of switches.
 8. The deployment unit ofclaim 4, wherein at least one of the first tier of switches comprises afirst tier switch of a second deployment unit.
 9. The deployment unit ofclaim 4, wherein each of the second portion of the first tier ofswitches directly connects to each first tier switch of a seconddeployment unit.
 10. The deployment unit of claim 9, wherein each of thefirst portion of the first tier of switches directly connects to eachfirst tier switch of one or more other deployment units.
 11. Thedeployment unit of claim 4, wherein each switch comprises a commoditynetwork switch or an application-specific integrated circuit (ASIC). 12.The deployment unit of claim 4, wherein a portion of the first tier ofswitches comprise top of rack (TOR) switches connected to a plurality ofcomputing devices in a network rack.
 13. The deployment unit of claim 4,wherein the deployment unit connects to an external network using a highradix interconnection network.
 14. The deployment unit of claim 4,wherein the deployment unit comprises a Clos-based network.
 15. A methodof connecting switches, comprising: providing a deployment unitcomprising at least a first tier of switches and a second tier ofswitches, each of the first tier of switches capable of being directlyconnected to each of the second tier of switches, a first portion of thefirst tier of switches directly connected to each of the second tier ofswitches, each of a second portion of the first tier of switchesdirectly connected to at least one of the second tier of switches; usingat least one processor of a computing device, determining a reduction ofdirect connections between at least a portion of the second tier ofswitches and the second portion of the first tier of switches to providea plurality of available second tier ports on the second tier ofswitches; reducing a number of the direct connections between the atleast a portion of the second tier of switches and the second portion ofthe first tier of switches according to the reduction; directlyconnecting additional switches to the first portion of the first tier ofswitches using the available second tier ports, the additional switchesincreasing a total number of host connections capable of being made bythe deployment unit; and directly connecting each of the additionalswitches to each of the second tier of switches.
 16. The method of claim15, wherein determining the reduction of direct connections includes:calculating a level of oversubscription for the deployment unit, thereduction of direct connections being based at least in part upon adetermined level of oversubscription.
 17. The method of claim 15,further comprising: connecting at least one of the second portion of thefirst tier of switches directly connect out of the deployment unit. 18.The method of claim 15, further comprising: directly connecting at leastone of the first portion of the first tier of switches to at least oneof a third tier of switches, each of the third tier of switches directlyconnecting out of the deployment unit, wherein network traffic betweendeployment units bypasses the second tier of switches.
 19. The method ofclaim 15, wherein at least one of the first tier of switches comprises afirst tier switch of a second deployment unit.
 20. The method of claim15, further comprising: directly connecting each of the second portionof the first tier of switches to each first tier switch of a seconddeployment unit.
 21. The method of claim 20, further comprising:directly connecting each of the first portion of the first tier ofswitches to each first tier switch of one or more other deploymentunits.
 22. A non-transitory computer-readable storage medium includinginstructions for designing a deployment unit, the instructions whenexecuted by at least one processor causing the at least one processorto: providing a deployment unit comprising at least a first tier ofswitches and a second tier of switches, each of the first tier ofswitches capable of being directly connected to each of the second tierof switches, a first portion of the first tier of switches directlyconnected to each of the second tier of switches, each of a secondportion of the first tier of switches directly connected to at least oneof the second tier of switches; reducing a number of direct connectionsbetween the at least a portion of the second tier of switches and thesecond portion of the first tier of switches to provide a plurality ofavailable second tier ports on the second tier of switches; directlyconnecting additional switches to the first portion of the first tier ofswitches using the available second tier ports, the additional switchesincreasing a total number of host connections capable of being made bythe deployment unit; and directly connecting each of the additionalswitches to each of the second tier of switches.
 23. The non-transitorycomputer-readable storage medium of claim 22, wherein the instructionswhen executed further cause the at least one processor to: determine alevel of oversubscription for the deployment unit, the number of thedirect connections being reduced being based at least in part upon thelevel of oversubscription.
 24. The non-transitory computer-readablestorage medium of claim 22, wherein each switch comprises a commoditynetwork switch or an application-specific integrated circuit (ASIC). 25.The non-transitory computer-readable storage medium of claim 22, whereina portion of the first tier of switches comprise TOR switches connectedto a plurality of computing devices in a network rack.
 26. Thenon-transitory computer-readable storage medium of claim 22, wherein thedeployment unit connects to an external network using a high radixinterconnection network.
 27. The non-transitory computer-readablestorage medium of claim 22, wherein the deployment unit comprises aClos-based network.